Variance of blood pressure in the normal population is composed of environmental influences and the cumulative effects of gene structure polymorphisms. Essential hypertension results from the combined influence of these components, whose respective importance can vary considerably from individual to individual. In the rare forms of hypertension due to a single gene abnormality, the environmental component is negligible and the genetic component is represented by a major transmitted gene abnormality with major effects on the phenotype. These rare forms of monogenic hypertension offer interesting models for the study of the genes involved in essential hypertension. The angiotensinogen gene represents the first example of a strongly supported implication of a gene in essential hypertension. The success of this strategy allows the possibility of identifying other genes in essential hypertension.